Gas discharge lamps and lasers fabricated by michromachining

ABSTRACT

A high pressure gas discharge lamp and the method of making same utilizing integrated circuit fabrication techniques. The lamp is manufactured from heat and pressure resistant planar substrates in which cavities are etched, by integrated circuit manufacturing techniques, so as to provide a cavity forming the gas discharge tube. Electrodes are deposited in the cavity. The cavity is filled with gas discharge materials such as mercury vapor, sodium vapor or metal halide. The substrates are bonded together and channels may be etched in the substrate so as to provide a means for connection to the electrodes. Electrodeless RF activated lamps may also be fabricated by this technique. Micro-lasers may also be fabricated by this technique as well.

This is a continuation of application Ser. No. 07/922,707, filed Jul.28, 1994 now abandoned.

BACKGROUND AND SUMMARY OF THE INVENTION

This invention is directed to high or low pressure gas discharge lampsused for lighting and display. This invention is also directed to amethod of fabricating such lamps by integrated circuit fabricationtechniques.

Gas discharge lamps (mercury vapor, sodium vapor, metal halide) are animportant segment of the lighting industry. It is well known that theluminous efficiency of gas discharge bulbs increases substantially athigh pressures (1-200 atmospheres). However, the containment of suchhigh pressures in a transparent vessel has presented significantproblems. Gas pressure is restricted in many instances because of thedifficulty of finding materials that are sufficiently lightweight, whileat the same time capable of withstanding high heat and pressures.Furthermore, such materials, to be practicable, must be capable ofrelatively inexpensive mass production. The usual construction of gasdischarge lamps is to suspend a transparent pressure and heat resistantdischarge tube by means of a metal framework within an outer glass bulb.

The present invention provides an entirely new paradigm for theconstruction of high pressure gas discharge lamps. Rather than andischarge tube mechanically suspended within an outer bulb, the presentinvention is directed towards methods of fabricating high pressure"microlamps" utilizing micromachining techniques which are similar tointegrated circuit fabrication techniques such as the etching of andbonding of planar substrates. The present invention is directed to animproved gas discharge lamp that can withstand very high pressures andthe method of making such a lamp by means of integrated circuitmanufacturing techniques. The lamp is manufactured from two planarsheets of temperature and pressure resistant transparent material. Acavity is etched in one or both of the sheets and electrodes aretherefore deposited in the cavity. The cavity is charged with a fillerappropriate to the type of lamp being manufactured such as mercury,sodium or metal halides. The two sheets are then bonded together so asto seal the cavity within the sheets. Contact may then be made with theelectrodes to activate the lamp. Electrodeless lamps activated by radiofrequency energy may also be manufactured by this technique. Miniaturegas discharge lasers may also be produced by this technique.

BRIEF DESCRIPTION OF THE DRAWINGS

For better understanding of the invention, reference is made to thefollowing drawings which are to be taken in conjunction with thedetailed description to follow:

FIG. 1 is a sectional diagram of an electrodeless, radio frequencyactivated lamp constructed in accordance with the present invention;

FIG. 2 is a plan view of the transparent substrates having a pluralityof lamp cavities disposed therein;

FIG. 3 is a sectional view of a lamp having opposed electrodesmanufactured in accordance with the present invention;

FIG. 4 is a sectional view of a side electrode lamp manufactured inaccordance with the present invention; and

FIG. 5 is a sectional view of a further embodiment of a side electrodelamp constructed in accordance with the present invention.

FIG. 6 is a sectional view of a side electrode lamp including melt zonesto further seal the electrodes; and

FIGS. 7 and 8 are sectional views of micro-lasers constructed inaccordance with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGS. 1 and 2 illustrate a high pressure lamps fabricated in accordancewith the present invention. As shown in FIGS. 1 and 2, a lamp 10 isfabricated from a first planar substrate 12 and a second planarsubstrate 14 which are bonded together by suitable means, as describedbelow, and each lamp 10 comprises a plurality of cavities 18 which formindividual luminescent micro-lamps. In FIGS. 1 and 2, the cavities 18are depicted as generally spherical and the substrates 12 and 14 aredepicted as circular in plan view. It should be kept in mind that thecavities and substrates may be of any size and shape. The substitutesare depicted as circular since handling equipment for circular plates isreadily available from numbers of integrated circuit manufacturingequipment. Cavities 18 may be square, rectangular or elongated channels.

FIG. 1 illustrates a lamp constructed in accordance with the presentinvention in its simplest embodiment, that of an electrodeless RFactivated lamp. The steps of manufacturing the lamp will also bediscerned from this figure. Planar substrate 14 is transparent andconsists of material suitable for containing the pressure andtemperature of an operating lamp, one such suitable material is quartz.Cavity 18 which comprises a half cavity 20 in substrate 14 and a halfcavity 22 in substrate 12 is formed by integrated circuit manufacturingtechniques.

The upper surface 24 of un-etched substrate 14 is covered by suitablemasking material, such as polysilicon, at the portions where etching isnot desired, as etching will occur at the unmasked portions. Thereafter,the masked substrate is exposed to an etchant such as hydrofluoric acidfor a time suitable to create cavity 20. The time and amount of exposureto the etchant may be adjusted, in the known manner, to provide thecavity size and shape desired. Upper substrate 12 is therefore maskedand etched in a similar manner to provide half cavity 22. For certainbonding processes, it is desirable that the surfaces of substrates 12,14 that are to be bonded together be planarized. This can beaccomplished by depositing phosphorus doped silicon dioxide andpolishing the surface. Alternatively a smooth surface can be obtained bydepositing phosphorous doped silicon dioxide and reflowing (heating) it.

After the formation of cavities 20 and 22 in substrates 12 and 14,respectively, cavity 20 is charged with a suitable luminescent material.In this embodiment, the lamp is a mercury lamp so that an appropriatesized drop of mercury 28 is placed in cavity 20. If cavity 18 is to becharged with a gas such as Argon, the bonding of substrates 12, 14 maytake place in an argon atmosphere at a pressure suitable for the finallamp. Accordingly, substrates 12 and 14 are placed in a pressure vesselat the appropriate argon pressure for the lamp to be manufactured.Thereafter, lower surface 26 of substrate 12 is bonded to upper surface24 of substrate 14. The bonding interface 16 may be formed by anysuitable means such as heat, chemical or anodic bonding. After thebonding is completed, the completed lamp 10 is removed from the pressurevessel and cavity 18 will contain an argon atmosphere having a charge ofmercury that will vaporize and form a mercury vapor lamp uponenergization. Since this is an "electrodeless lamp", the mercury isvaporized and luminesces by application of RF energy from external RFelectrodes 30.

FIG. 3 illustrates how the present invention is used to produce a lamphaving electrodes which is a more common design than the RF lamp ofFIG. 1. In FIG. 3, the same reference numerals are used to indicate thesame structure that of FIG. 1. In FIG. 3, each half cavity 20, 22 insubstrates 14, 12 is produced by masking and etching in a similar manneras the lamp of FIG. 1. After the etching of the half cavities 20, 22 afurther manufacturing step takes place: the deposition of electrodes 40and 42 in cavities 20, 22 respectively. The electrodes may be composedof any suitable electrode material, such as tungsten, and are depositedby known metal deposition processes, i.e. masking, etching anddeposition of material. Since electrodes 40, 42 must be connected tocurrent, electrical connection must be made to electrodes 40, 42.Connection with electrode 42 is made by etching a channel 46 in theupper surface 44 of substrate 12. In this case, upper surface 44 ismasked at the areas to remain unetched and an etchant acts on theunmasked portions to etch channel 46 into surface 44 down to theelectrode 42 to expose its rear surface. Thereafter, by deposition andpatterning, a coating of conductive material 47, which may be a metallicor non-metallic conductor is applied in channel 46. Coating 47 extendsfrom the electrode 40, 42 to the outer surface of the respectivesubstrates. In order to maintain the pressure integrity of cavity 18,"plug" material 48 such as glass is deposited over metal layer 46 tostrengthen cavity 18 and to render the outer substrate surfaces flush.Thereafter, substrates 12, 14 are charged with the appropriateluminescent material and bonded as is described above with respect tothe lamp of FIG. 2. Connection of electrodes 40, 42 to an appropriatesource of current will cause the lamp to illuminate. Additional pairs ofelectrodes, such as starter electrodes, may also be deposited andconnected in a like manner.

FIG. 4 illustrates another embodiment of the present invention in whichthe electrodes are disposed in side-by-side relationship, the samereference numerals are again used to denote similar structure. As shownin FIG. 4, the upper substrate 12 is formed in a similar manner to theprevious embodiments. However, lower substrate 14 is first masked andetched so as to form a relatively wide rectangular cavity 60 andelectrodes 62, 64 are deposited on its flat lower surface. A seconddeeper central cavity 66 is then etched into substrate 14 by suitablemasking and etching techniques, and by use of an etchant which does notattack the material of electrodes, 62, 64. These electrodes willoverhang cavity 66. Thereafter, the lower surface of substrate 14 isetched to create channels 68, 70 which contact the lower surface ofelectrodes 64, 62 respectively. A conductive layer 72, 74 may then bedeposited in channel 68, 74 for electrical connection to electrode 64,62. Thereafter, plug material 76, 78 may be used to fill in the gapbetween the lower surface of substrate 14 and metallic layers 72, 74.The cavity 18 is then charged. The lower surface of substrate 12 is thenbonded to substrate 14 in the manner described above.

The present structure and methodology also lends itself to themanufacture of miniature fluorescent bulbs which utilize a phosphorcoating which, when energized by the ultraviolet rays generated bymercury vapor, will fluoresce. In FIG. 4, the phosphor layer isdeposited on the upper surface of substrate 12. The lamp shown in FIG. 4has both electrodes disposed in a single substrate and the electricalconnections are made on a single substrate. It is also noted that in theconstruction of this type of lamp, there need not be a cavity 22disposed in substrate 12 because if cavity 60 is large enough, uppersubstrate 12 may be merely a flat piece of quartz or glass.

FIG. 5 shows yet another variant of the side electrode lamp of FIG. 4.In the lamp shown in FIG. 5, the lower substrate 14 further includesdeposition of layers 82, 84 of P-glass (phosphorus doped glass) whichcover electrodes 62 64- to a level equal to the upper surface ofsubstrate 14. Thereafter, the upper substrate 12 has channels 86, 88etched through substrate 12 and through the P-glass layers 82, 84 so asto expose the upper surface of electrodes 62, 64. Thereafter, conductivelayers 90, 92 and plug material 94, 96 are deposited in channels 86 and88. This arrangement permits contact with and connection to electrodes62, 64 through the upper surface of the device rather than the lowersurface of the device as shown in FIG. 4. The use of P-glass alsoprovides an efficient sealing of the electrodes to the substrate.

FIG. 6 illustrates a side electrode lamp 100 which is constructedsimilar to that of FIG. 4 with the addition of melt zones 102, 104 whichare used to further seal the electrodes within the substrates. Meltzones 102, 104 are formed by exposing the completed lamp to a CO₂ laserwhich will melt the quartz substrates to seal the tungsten electrodesfirmly therewithin. Additionally, a layer of molydenum may be added tothe tungsten electrodes to aid in sealing. The molydenum layer willassist the substrate/electrode seal with or without melt zones 102, 104.

As noted above, lamps fabricated by this methodology may be any type ofgas discharge lamp. The material suitable for the substrates is also notrequired to be quartz as any transparent material capable ofwithstanding the heat and pressure that may be used. In certaincircumstances, glass is a suitable substrate for use with the certaintypes of lamps. The number of cavities disposed in the substrate may bevaried in accordance with the requirements of the application. The lampsmay be used as illumination or as display. Finally, the lamps can beenergized all at once or circuitry can be disposed on the substrate soas to provide non-simultaneous activation of the various microlampsdisclosed in the substrate.

FIG. 7 illustrates a micro-laser constructed in accordance with theinvention. Micro-laser 120 is constructed, as are the previous gasdischarge lamps, from an upper substrate 122 and a lower substrate 124.Lower substrate 124 has a first, relatively shallow channel 126 disposedthereon and a second deeper channel 128 at its centermost portion. Byetching and deposition techniques similar or identical to thosedescribed above extending into channel 128 are first and secondelectrodes 130, 132. Similarly upper substrate 122 has a channel 134formed therein. Mounted to the exterior of substrate 124 is a partiallyreflective mirror 136 formed by metal deposition, photlithographictechniques and etching. Disposed on the upper substrate 122 is a fullyreflective mirror 138. A central cavity 140 is formed by the halfcavities 128, 134 and may be charged with gaseous material which willlase under application of electrical input applied on electrodes 132,130.

When a discharge is created within cavity 140 the action of mirrors 136and 138 will provide a lasing action such as to cause the atoms of thegaseous material to lase as is known to those skilled in the art of gasdischarge lasers. Thus, partially reflective mirror 136 and fullyreflective mirror 138 form an optical cavity for the excitation of atomsof the gaseous fill material. Suitable gaseous fill material are thoseusually utilized in large size gas discharge lasers.

Such material includes CO₂, Helium-Neon, Argon and the like. By suitableselection of the gaseous material and by the size and properties of theoptical cavity, the lasing frequency may be adjusted over a widefrequency range. Such frequencies can range from the infrared to theultraviolet. Gas discharge lasers are capable of generating light of ablue frequency or higher which, at this date, are difficult for solidstate devices. Micro-lasers constructed in accordance with thisinvention can also be "electrodeless". Such lasers can be pumped throughthe application of external RF or microwave energy.

FIG. 8 shows another embodiment of a micro-laser constructed inaccordance with the present invention. In FIG. 8 the same referencenumerals are used to indicate the same structure as that of FIG. 7. Inthe laser structure of FIG. 7, mirrors 136 and 138 were disposedexternal to the substrates. The present invention does not require thatthe mirrors be disposed externally of the optical cavity. FIG. 8illustrates a laser structure including mirrors disposed in cavity 140.In FIG. 8 a partially reflective mirror 144 is disposed on the lowersurface of cavity 128 in lower substrate 124. A fully reflective mirror146 is disposed on the upper surface of cavity 134 in upper substrate122. The mirrors used in the structures of FIG. 7 and FIG. 8 may also beconstructed from metallic materials which may be deposited within thesubstrates. It is to be further noted that the mirrors utilized inconstruction with the micro-lasers of FIG. 7 and FIG. 8 need not haveplanar surfaces. The mirror surfaces could be curved in accordance withany special requirements. Furthermore the mirrors can be spaced apartfrom the substrates and need not be mounted thereto. A particularlysuitable substrate material for use in a laser device is sapphire. Sincesapphire is crystalline anisotropic etching can provide mirrors withsuperior optical qualities.

The above described structures and methodology are merely illustrativeof the principles of the present invention. Numerous modifications andadaptations thereof will be readily apparent to those skilled in the artwithout departing from the spirit and scope of the present invention andthe appended claims.

What is claimed is:
 1. A gas discharge light emitting devicecomprising:a) first and second substrates of continuous material capableof withstanding heat and pressure; b) at least one of said substrateslight transmissive; c) said substrates having confronting planarsurfaces in contact with each other; d) at least one of the substrateshaving at least one cavity disposed therein, the cavity having anopening at the planar surface of the substrate; e) a bonded interfacedisposed substantially across said substrates at their confrontingsurfaces, except at said cavity; f) luminescent gas discharge materialdisposed in said cavity; and g) means for energizing said luminescentmaterial.
 2. The gas discharge lamp as claimed in claim 1, furtherincluding a phosphor layer disposed on the surface of at least one ofsaid substrates.
 3. The gas discharge lamp as claimed in claim 1 furtherincluding first and second at least partially reflective mirrors so asto form a laser.
 4. The gas discharge lamp as claimed in claim 1 whereinthe bonded interface is heat bonded.
 5. The gas discharge lamp asclaimed in claim 1 wherein the bonded interface is anodically bonded. 6.The gas discharge lamp of claim 1 in which the means for energizing saidluminescent material comprises first and second electrode means disposedin said cavity.
 7. The lamp as claimed in claim 6, further includingelectrically conductive means extending through at least one of saidsubstrates for electrical connection with said at least one electrode.8. The gas discharge lamp as claimed in claim 7, further includingchannels disposed in at least one of said substrates through which saidelectrically conductive means extend.
 9. A lamp comprising:a firstcontinuous planar substrate having an upper and a lower surface; asecond continuous planar substrate having an upper and a lower surface;at least one of said first and second planar substrates being lighttransmissive; said upper surface of said first substrate being in faceto face contact with the lower surface of said second substrate; acavity disposed in at least the first substrate, the cavity having anopening in the upper surface of the first substrate, or the secondsubstrate, the cavity having an opening in the lower surface of thesecond substrate; a bonded interface disposed across said upper surfaceof said first substrate and said lower surface of said second substrateexcept at the cavity, the cavity sealed thereby; luminescent meansdisposed in said cavity; and first and second electrode means disposedin said cavity for actuating the luminescent means in said cavity. 10.The lamp as claimed in claim 9, further including at least one channeldisposed in at least one of said first and second substrates, saidelectrodes being disposed in said at least one channel.
 11. The lamp asclaimed in claim 9, further including a channel disposed in at least oneof said first and second substrates, said channel extending from thelower surface of said substrate to the upper surface of said substrate.12. The lamp as claimed in claim 9, further including channels disposedin at least one of said first and second substrates at the interfacetherebetween and extending along the interface, said first and secondelectrodes being disposed in said channels.
 13. The lamp as claimed inclaim 12, further including planarizing means disposed atop saidelectrodes so as to provide a surface which is coplanar with saidinterface.
 14. The lamp as claimed in claim 12, wherein a portion of atleast one of said first and said second substrates is melted so as toseal said electrode therewithin.